The present invention relates to antimicrobial hydrogel-forming absorbent polymers. The invention also relates to processes for producing such absorbent polymers. The present invention has particular applicability to absorbent articles such as diapers, adult incontinence pads, sanitary napkins, and the like.
A wide variety of disposable absorbent articles designed not only to be efficient in the absorption of body fluids such as urine, blood, menses and the like, but also to be sanitary and comfortable in-use, are known in the literature. Disposable absorbent products of this type generally comprise a fluid-permeable topsheet material, an absorbent core, and a fluid-impermeable backsheet material. Various shapes, sizes and thicknesses of such articles have been explored in an attempt to make their use more comfortable and convenient.
For some time now, studies for such disposable absorbent articles have been primarily focused on the absorptive capacity of the article. As a result, various absorbent polymers with high absorptive power have been developed. Such known absorbent polymers (also known as hydrogel-forming absorbent polymers) are capable of absorbing from about thirty to sixty grams of water per gram of polymer.
More recently, research has been focused on the removal of foul odors and the prevention of skin diseases such as dermatitis, rash and redness caused by wearing a disposable absorbent article for a relatively long time. Many body fluids have an unpleasant odor, or develop such odors when in contact with air and/or bacteria for prolonged periods. Additionally, urine and/or other exudates absorbed into the absorbent article are converted to ammonia by urease produced by skin-flora, i.e., a group of normal microorganisms on the skin. This ammonia, in turn, causes dermatitis, rash and/or other forms of skin irritation. Such disease of the skin in infants can be a serious medical matter which, in extreme cases, can result in death.
Antimicrobial agents and bactericides are chemical compositions that are used to prevent microbiological contamination and deterioration of products, materials, and systems. Particular areas of application of antimicrobial agents and compositions are, for example, cosmetics, disinfectants, sanitizers, wood preservation, food, animal feed, cooling water, metalworking fluids, hospital and medical uses, plastics and resins, petroleum, pulp and paper, textiles, latex, adhesives, leather and hides, paint slurries, and disposable diapers.
For example, Japanese Patent 4-17058 discloses a disposable diaper which is said to prevent the occurrence of diaper rash caused by the growth of saprophytes such as the bacteria colibacillus and Candida. The disclosed disposable diaper consists of a water-permeable top sheet, a water-impermeable back sheet, and a water-absorbent layer sandwiched between these sheets. The water-absorbent layer is further disclosed as consisting of a) an ammonia-adsorbent, water-absorbent organic polymer selected from the group consisting of polyacrylate polymers, starch-acrylonitrile graft copolymer hydrolizates, starch-acrylic acid graft copolymers, polyvinyl alcohol-acrylate copolymers, polymers produced by further crosslinking of a crosslinked acrylate with a crosslinking agent, and modified carboxymethyl cellulose; and b) benzalkonium chloride and/or chlorhexidine gluconate, contained within the water-absorbent organic polymer. The reference further discloses forming the organic polymer/bactericide material by combining the starting materials of the organic polymer (e.g., microparticulate silicon dioxide, a copolymer such as crosslinked potassium polyacrylate, and a cross-linking agent such as ethylene glycol diglycidyl) and the bactericide. The resulting mixture is then heated to bring about a crosslinking reaction, thereby forming a crosslinked structure, the bactericide being incorporated within the structure.
While the diaper disclosed by Japanese Patent No. 4-17058 is said to result in absorption by the organic polymer of ammonia contained in the wearer""s urine, and the bactericide is said to inhibit the production ammonia (formed by hydrolysis of the urea contained in the urine) by bacteria, we have discovered certain disadvantages with this technology.
For example, because such surfactant based antimicrobial agents or bactericides tend to decrease the surface tension of the liquid absorbed by the absorbent polymer or core, it was discovered that those antimicrobial agents or bactericides cause a significant re-wet or leakage problem of the liquid when they are used with a synthetic nonwoven coverstock (i.e., topsheet and/or sub-layer between topsheet and absorbent core) in disposable absorbent products. More specifically, the liquid temporarily stored in the core tends to return to the coverstock because of the lowered surface tension of the absorbed liquid by the surfactant, thereby causing the re-wet and/or leakage problems.
Based on the foregoing, there is a need for an antimicrobial hydrogel-forming absorbent polymer that minimizes the change of the surface tension of the liquid absorbed by the absorbent core.
There is also a need for an absorbent article product containing such an antimicrobial hydrogel-forming absorbent polymer, which maintains the antimicrobial activity in a region away from the wearer""s skin, before and after wetting.
The present invention is directed to an antimicrobial hydrogel-forming absorbent polymer comprising a hydrogel-forming absorbent polymer, and an antimicrobial comprising a 1-hydroxy-2-pyrrolidone derivative represented by the formula (I); 
wherein R1 represents an alkyl group having 1-17 carbon atoms, alkenyl group having 2-17 carbon atoms, cycloalkyl group having 5-8 carbon atoms, bicycloalkyl group having 7-9 carbon atoms, cycloalkyl-alkyl group wherein the alkyl group has 1-4 carbon atoms and the cycloalkyl group may be substituted with an alkyl group having 1-4 carbon atoms, aryl group, aralkyl group with an alkyl group having 1-4 carbon atoms, aryl-alkenyl group with the alkenyl group having 2-4 carbon atoms, aryloxyalkyl or arylmercaptoalkyl group with the alkyl group having 1-4 carbon atoms, benzhydryl group, phenylsulfonylalkyl group with the alkyl group having 1-4 carbon atoms, furylalkenyl group with the furyl or alkenyl group having 2-4 carbon atoms, wherein the above-mentioned aryl residual group may be substituted with an alkyl group having 1-4 carbon atoms, alkoxy group having 1-4 carbon atoms, nitro group, cyano group, or a halogen atom; R2 represents a hydrogen atom, alkyl group having 1-4 carbon atoms, alkenyl group having 2-4 carbon atoms, halogen atom, phenyl group, or benzyl group; and X+ represents an organic base, alkali metal ion, ammonium ion, alkaline earth metal ion, or a divalent to tetravalent cationic ion.
The present invention further relates to a process for making such an antimicrobial hydrogel-forming absorbent polymer, the process comprising the step of applying an antimicrobial comprising a 1-hydroxy-2-pyrrolidone derivatives represented by the formula (I) onto a hydrogel-forming absorbent polymer.
The present invention further relates to a disposable absorbent article comprising the antimicrobial hydrogel-forming absorbent polymer.
These and other features, aspects, and advantages of the present invention will become evident to those skilled in the art from a reading of the present disclosure and accompanying drawings with the appended claims.